Fibonacci -- suggestions please

This is a discussion on Fibonacci -- suggestions please within the C++ Programming forums, part of the General Programming Boards category; Hello all. I am still pretty new to C++ and I made this Fibonacci sequence thing. What would you recommend ...

  1. #1
    Registered User Kudose's Avatar
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    Fibonacci -- suggestions please

    Hello all. I am still pretty new to C++ and I made this Fibonacci sequence thing.

    What would you recommend to prevent a segmentation fault if the first to vector elements are not populated, or rather, how would you ensure the first two elements were populated?

    Code:
    #include <iostream>
    #include <vector>
    #include <iomanip>
    
    using namespace std;
    
    int main(){
    	vector<double> fib;
    	double stop = 200;
    	double i = 1;
    
    	fib.push_back(1);
    	fib.push_back(1);
    
    	while(i++ <= stop)
    		fib.push_back(fib[i-1] + fib[i-2]);
    
    	for(i = 0; i < fib.size(); i++)
    		cout << setprecision(50) << fib[i] << endl;
    
    	cout << endl;
    
    	return 0;
    }
    TIA!

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    I don't know what your question is. If the first two elements aren't populated, you can't do the Fibonacci sequence, so you shouldn't ever get into the situation.

    But I suppose you can check that fib.size is at least 2 before trying to do the loop.

  3. #3
    Registered User Kudose's Avatar
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    I guess what I am really asking is: is that how you would implement it , if there was some way I was missing that the first two values could be filled or a better way the program could be written.

  4. #4
    CSharpener vart's Avatar
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    Quote Originally Posted by Kudose View Post
    I guess what I am really asking is: is that how you would implement it , if there was some way I was missing that the first two values could be filled or a better way the program could be written.
    but you have it

    Code:
    fib.push_back(1);
    fib.push_back(1);
    What you have wrong - is

    double i = 1;

    1. Why index is double?
    2. Why it is 1 if you want to access element i-2?
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  5. #5
    Registered User Kudose's Avatar
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    1. It should be an int, it was left over from messing around.

    2. I see the logic error in that. i should be 2.

    Thanks.

  6. #6
    Algorithm Dissector iMalc's Avatar
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    Quote Originally Posted by Kudose View Post
    2. I see the logic error in that. i should be 2.
    No, you had it right as it was. It is initialised to 1 and then incremented to two in the while loop condition.
    The only bug is using double instead of int.
    An explicit push_back of the two 1's before the loop gets underway is the sensible way to do it, if you need the values all in a vector. In your code example you can just output them as you go and forget the vector though.
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